1. Field of the Invention
The present invention relates to ink jet recording apparatuses. More specifically, the present invention relates to a cap unit including a cap for covering one surface of a recording head in which ejection ports are provided (hereinafter referred to as an “ejection port surface”).
2. Description of the Related Art
A cap unit of an ink jet recording apparatus prevents and eliminates clogging in ejection ports by covering an ejection port surface to form an enclosed space and causing a suction pump to generate a negative pressure in the enclosed space to forcibly discharge ink from the ejection ports. The pressure in the cap at this time can reach 0.2 atm. FIG. 9 shows the structure of a conventional cap unit. A cap 101 in FIG. 9 is made of a soft material, such as rubber, and is brought into intimate contact with an ejection port surface to form an enclosed space. The cap 101 has holes corresponding to tubular ink discharge ports 103 and air communication ports 104 provided in a cap holder 102. When the inner circumferential surfaces of the holes in the cap are brought into intimate contact with the outer circumferential surfaces of the ink discharge ports 103 and air communication ports 104, an enclosed space is formed by the ejection port surface and the cap. Therefore, when the suction pump produces a negative pressure in the enclosed space, the cap 101 is deformed. More specifically, the outer circumferential side wall of the cap 101 leans inward, and the bottom of the cap 101 tends to be deformed toward the ejection port surface. At this time, in an apparatus in which particularly great negative pressure is produced in the cap 101, the deformation tends to be excessive. As a result, improper sealing may occur, failing to form an enclosed space and causing suction failure. Furthermore, if the deformation of the bottom of the cap 101 due to friction or the like between the cap 101 and the cap holder 102 remains after the cap is opened, it is difficult to form an enclosed space in the next capping operation.
Japanese Patent Laid-Open No. 2001-105615 discloses a cap in which a portion that is brought into contact with an ejection port surface is formed such that it covers reinforcing ribs formed on a cap holder. In this cap, the portion formed such that it covers the reinforcing ribs formed on the cap holder is engaged with an engaging portion formed on the cap holder, thereby preventing deformation of the cap.
Japanese Patent Laid-Open No. 2001-105615 also discloses that the cap and the cap holder are integrally molded by coinjection molding. Because the contact surfaces of the cap and cap holder are bonded, deformation of the cap can be prevented.
In the cap disclosed in Japanese Patent Laid-Open No. 2001-105615, deformation of the portion that is brought into intimate contact with the ejection port surface, i.e., a portion near the side wall of the cap, can be suppressed. However, deformation of the bottom of the cap resulting from long-term use cannot be suppressed. Thus, it may be difficult to form a sufficient sealing surface with respect to the ink discharge ports and the air communication ports.
The cap is deformed by a negative pressure every time the suction operation is performed. Thus, the contact surfaces of the cap and cap holder, which are integrally molded by coinjection molding, can be separated. Furthermore, because the materials of the cap used in the coinjection molding are limited, selection of the materials taking functions, such as gas permeability, resistance to ink, and attachment to the ejection port surface, into consideration is difficult. In addition, because the cap and the cap holder are integrally molded, disassembling maintenance is difficult.